(1) Field of the Invention
The present invention relates to a digital tape measure in which a tape is built in a case body and is movable being drawn out and rewound in through an aperture of the case body, and a detected amount of movement of the tape is converted to an electric signal so that a length measured may be digitally displayed in an optional system of units.
(2) Prior Art
In a known digital tape measure in which a photographic tansfer (conversion) element is used when converting an amount of movement of a tape to an electric signal, a light is projected on marks of the tape, and by receiving a reflected light of the projected light, a detected amount corresponding to the amount of movement of the tape is counted for length measurement, it is usual that the amount of movement of the tape drawn out of the case body is measured by establishing an outlet, i.e., aperture formed on a front side of the case body as a starting point for measurement, and that photoelectric detecting means comprising a photoelectric transfer element, computing means for computing signals detected by the detecting means, and displaying means for displaying a computed result, each forming essential parts of the digital tape measure, are solidly fitted in the case body which the tape is built in.
Under such arrangement of the conventional digital tape measure, a problem exists in that a rather troublesome or intricate operation is required at the time of measuring a full length of an object to be measured with the tape stored in the case body and carrying out a further measurement for dividing the full length into several equal parts.
For example, in case that a full length of an object measured by a tape measure capable of measuring 30 m at maximum is 10.5 m and it is required to divide this full length into seven equal parts of 1.5 m each, the tape is once stored in the case body after completing the measurement of the full length and the marking for such division is carried out for every 1.5 m by moving the case body from an end portion of the measuring object.
In such operation, it is necessary to apply a tension to the tape since the tape is usually loosened when measuring a large distance, an accurate measurement being affected thereby. In the operation, as the starting point is established at the outlet of the case body, it is required to coincide the starting point with a measuring point of the full length by moving the case body back and forth while tensioning the tape itself, which is a difficult operation particularly when measuring a long (or large) distance because it is impossible to give the tension to the tape only by pulling the case body. Furthermore, unless every dividing length is measured by the tape which is in the same state of tension as the time of measuring the full length, a total length of each divided parts is not coincident with the full length.
Thus, according to the known digital tape measure, since such means as photoelectric detecting means are fitted in the case body and the amount of movement of the tape is detected by establishing the outlet for drawing out the tape as a starting point for measurement, a measurable length is limited to a length between the outlet and an end of the tape, and as a result the measuring method is restricted either to a measurement by fixing the case body while moving the tape or to a measurement by fixing the end of tape while moving the case body, thus being impossible to solve the above-discussed problem.